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IAMI — For months now, the Centers for Disease Control and Prevention has been warning pregnant women not to travel to several dozen countries where the Zika virus is spreading. On Monday, the Atlanta-based agency cautioned American women who are pregnant not to travel to a part of the United States.

CDC Director Dr. Tom Frieden urged women who are pregnant to avoid a roughly one-square-mile section of Miami-Dade County where it is believed local mosquitoes are transmitting Zika. He said he believed it marked the first time the CDC had issued a health-related travel advisory for the mainland United States.

The CDC has been warning for months that some local transmission of Zika in the 50 states was likely, though it has insisted aspects of the US lifestyle — houses with screened doors and windows, homes and vehicles with air conditioning — should lower the risk of large outbreaks.

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“Nothing that we’ve seen indicates widespread transmission, but it’s certainly possible there could be sustained transmission in small areas,” Frieden said during a briefing for reporters.

“This is particularly a risk for people who don’t have screens or air conditioning and who live in crowded spaces.”

So far, Florida has detected 14 people who have contracted the virus in the country’s first Zika outbreak. These people have not traveled to places where the virus is spreading, and it is not believed they were infected through having sex with someone infected with the virus.

The area where Zika is believed to be spreading is located north of Miami’s downtown core, known as Wynwood.

Frieden described it as a mixed area, with some homes and some industrial properties, some affluent parts, and some areas that are “economically stressed.” That diversity adds to the challenge of trying to control mosquitoes in the area, he said.

Attention has focused on Wynwood because two of the first cases work in the area. Testing of other people from the two workplaces as well as the surrounding neighborhood has turned up additional cases, at least six of whom tested positive but reported having no symptoms.

The CDC director said despite aggressive efforts by Florida to lower populations of Aedes aegypti mosquitoes — the main species that spreads Zika — the state has seen no reduction in the numbers caught in the traps it sets. That suggests the efforts aren’t working.

Frieden offered several explanations, including the possibility that the mosquitoes may have developed resistance to the chemicals being used to control them. Testing to see if that is the case will take at least a week and perhaps three or more.

Pregnant women who live in the affected area should routinely take steps to avoid being bitten by mosquitoes, and should practice safe sex to prevent sexual transmission of the virus, the CDC said. It suggested pregnant women without symptoms of Zika who live in or frequently travel to this part of Miami-Dade County should be tested for Zika infection in the first and second trimesters of their pregnancies.

And women and men who have traveled to this area should wait at least eight weeks before trying to conceive a child; men who have had symptoms should wait at least six months.

Florida Governor Rick Scott announced that he has asked the CDC to send an emergency response team to help Florida’s department of health with its investigation and mosquito control efforts. Previously the state had only asked the CDC to provide it with the services of an expert epidemiologist. By Tuesday, the CDC’s team in Florida will include eight experts, Frieden said.

Wynwood is home to a large Puerto Rican community. Officials here say they have enlisted community organizations to help spread information about the virus and mosquito control.

“Everybody’s concerned about it,” said Luis De Rosa, the president of the South Florida Puerto Rican Chamber of Commerce. “Education has been the key to all of this.”

The chamber is located in the area where officials believe Zika has been transmitted, but De Rosa said he hasn’t heard from anyone that they are avoiding the area.

The week-old outbreak is already larger than Florida’s earlier experience with another mosquito-spread virus, chikungunya. In 2014, a dozen people in Miami-Dade, and neighboring Broward, Palm Beach, and St. Lucie counties contracted chikungunya, which causes more severe illness than Zika but is not linked to birth defects.

Of the 10 new Zika cases, six had no symptoms and were identified through a door-to-door survey the department of health is doing to assess how far Zika has spread. The statement did not indicate the genders of the people. And Florida has not revealed if any of the people infected locally are pregnant women.

Dr. Karla Maguire, an obstetrician-gynecologist at the University of Miami who is 13 weeks pregnant, said Zika has “hit home both personally and professionally.”

For months, Maguire, who does not live in Wynwood, has been talking about Zika with her patients and what they could do to minimize their risk. She was also taking precautions herself: wearing long sleeves and pants and applying mosquito repellent, and forgoing the long nightly walks on the beach that she did during a previous pregnancy a few years ago.
Now, she said, “it’s not as abstract.”

With local transmission confirmed, Maguire said she is putting on more repellent every day and spending less time outdoors. She said her patients seems to be responsive to her advice, but that she has had to tell them that it is safe for them to use DEET during their pregnancies and that it is the most effective way to keep mosquitoes at bay.

One challenge with Zika, Maguire said, is that so much is not known. Women in their third trimesters want to know if they’re safe, for example. And while experts think fetuses in the first trimester are most vulnerable, they aren’t sure what kind of longterm effects there might be for a fetus infected with Zika during the third trimester.

Aedes aegypti mosquitoes are found throughout Florida and other states on the Gulf Coast. Although the virus typically generally causes only a mild illness — and often no symptoms at all —  it can cause serious birth defects in fetuses when it infects pregnant women.

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Blanca Che, 45, who lives in a pocket of Wynwood full of single-story homes, said she had seen crews going door to door several times in the past week distributing fliers about mosquito control and Zika. She said the crews had been knocking on doors and returning later if no one answered.

She said her family always made sure to empty any standing water in the yard. She said she wasn’t that concerned about Zika in her neighborhood because she knew it would never spread like it has in Latin America.

“We’re taking all necessary precautions,” she said as she took out the trash, wearing a tank top and shorts.

On Monday morning, De Rosa, of the South Florida Puerto Rican Chamber of Commerce, walked through a park in the neighborhood named after legendary Puerto Rican baseball player Roberto Clemente to make sure there was no litter that could be collecting water and provide a breeding ground for mosquitoes.

De Rosa said it was important for everyone to do their part to fight Zika because of how unpredictably and quickly it could pop up.

“Today it’s Wynwood, tomorrow it could be Orlando,” he said.

Helen Branswell reported from Boston. 

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  • Two weeks ago, in an elaborate mousetrap of nonsensical logic, the CDC said that where Zika is concerned there is no reason not to go to Rio for the Olympics, but now women should avoid Florida? It makes me wonder if the experts at the CDC know how this virus transmission thing works.

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